1. Field of the Invention
The present invention relates to light-weight tubeless pneumatic tires having excellent anti-airleak properties.
2. Description of Related Art
A typical structure of a tubeless pneumatic tire is shown in FIG. 10.
The tubeless tire includes a carcass ply 1 defining the carcass of the tire and comprising a carcass cord web made of organic fiber such as of nylon, steel wire or the like and a topping rubber covering the opposite surfaces of the carcass cord web. The carcass ply 1 extends from a tread portion through a shoulder portion and sidewall portion to a bead portion, and is turned up around a bead core 2 outwardly from the inside of the tire in the axial direction. The entire interior surface of the carcass ply 1 is lined with an inner liner 3 mainly made of butyl rubber which is excellent in air impermeability for the prevention of air charged in the tire from leaking therefrom, whereby the tubeless tire maintains a predetermined air pressure therein. As shown in FIG. 10, the tire further includes a tread reinforcing belt 4 such a breaker or belt layer disposed on the outer surface of the carcass ply 1, and a rim 5.
Such a tubeless tire is light in weight because it has no tube, and in recent years, a further weight reduction of tires has been desired for achieving an energy-savings when the vehicle is operated.
Japanese Unexamined Patent Publication No. 4-90902 (1992) discloses a tubeless pneumatic tire which is made light by separately disposing therein inner liners in regions of the right and left sidewall portions thereof, i.e., by providing no inner liner in a region of the tread portion thereof. However, the major part of the interior surface of the tire is still lined with the inner liner and, therefore, the weight reduction of the tire is not significant.
On the other hand, Japanese Unexamined Patent Publication No. 6-156007 (1994) discloses a tubeless pneumatic tire comprising a carcass 9 consisting of a carcass cord web 7 and a topping rubber 8 of a butyl-based rubber covering the opposite surfaces of the carcass cord web 7, as shown in FIG. 11 (enlarged view of a bead portion) and FIG. 12 (sectional view of the carcass). In FIG. 11, reference numeral 10 denotes the bead core. Since the topping rubber 8 is formed of a butyl-based rubber which is excellent in air impermeability and hence the carcass 9 per se exhibits the function of an inner liner, the inner liner can be entirely dispensed with. Thus, a satisfactory weight reduction can be achieved.
However, butyl-based rubbers have poor vulcanizability and adhesiveness in comparison with diene-based rubbers. If a tire has a topping rubber 8 entirely formed of a butyl-based rubber, the butyl-based rubber comes into contact with a ply layer (e.g., breaker ply, sidewall rubber or the like) disposed outside the carcass. This may cause the ply layer to be readily separated from the carcass, thereby causing a deterioration in the durability of the tire.